Incorporation of full-fat flaxseed, and to a lesser extent, canola seed in diets to produce n-3-enriched products has attracted interest in the poultry industry. However, high amounts of nonstarch polysaccharides (NSP) in oilseeds compromise their nutritive value. The objectives of the current research were to develop enzyme supplements effective in cell wall depolymerization and viscosity reduction, particularly in flaxseed; to evaluate the effects of enzyme addition and feed processing on oil utilization and egg n-3 fatty acid deposition in broiler chickens and laying hens fed oilseed-containing diets; to characterize the NSP hydrolysis products and to investigate the effects of diet type and enzyme addition on growth performance and the incidence of necrotic enteritis (NE) in broiler chickens challenged with Clostridium perfringens. Results showed that diets containing high levels of flaxseed reduced egg production and shell quality in laying hens, and impaired final body weight and feed conversion ratio (FCR) in broiler chickens. Reducing flaxseed particle size via grinding did not improve the growth performance of broiler chickens, whereas diet pelleting showed more pronounced and beneficial effects in improving the nutritive value of flaxseed, particularly when intact seeds were used. Multicarbohydrase supplementation resulted in a significant depolymerization of cell wall polysaccharides in soybean, canola and flaxseed meals, which was followed by the production of water-soluble NSP hydrolysis products, and the reduction of flax mucilage viscosity in vitro was also evident. Enzyme addition to flaxseed-containing diets improved FCR of broiler chickens and egg production performance of laying hens, and facilitated egg n-3 fatty acid deposition. The C. perfringens challenge caused intestinal NE lesions and increased the mortality of broiler chickens with the highest NE mortality and intestinal C. perfringens counts observed in those fed flaxseed-containing diets. Enzyme supplementation to diets containing high levels of water-soluble NSP (wheat/barley- or wheat/barley/flaxseed-based) facilitated post-disease compensatory growth in pathogen challenged birds. This was accompanied by a numerical reduction of intestinal C. perfringens by 1.4 log10 cfu/g in birds fed the flaxseed-containing diets. Such findings indicated that enzyme addition may be used as a nutritional strategy to reduce the risk of NE development in broiler chickens.